Even a tiny local credit union is great if they're part of the co-op.

The vast majority of credit unions in the U.S. are, and you can use any co-op branch or ATMs just like your home credit union's branches or ATMs.

It's brilliant, and in my experience, so much more accessible than the giant banks who are often regionally concentrated.

There are limitations, it's not always just like your home credit union. One of the reasons one might go to a bank branch when we have ATMs and online banking is to get a cashier's check, which can't be done through co-op. My online credit union can FedEx them overnight so it's not too bad, but I switched away from a local credit union when I moved because they weren't able to do services like that except at a branch.

My mom got a cashier's check through the co-op in March to buy her house. She's in New Hampshire and her credit union is in Oklahoma.

I don't know why it didn't work for you, but it was no trouble for her.

In my experience accessing my account after moving has been a huge issue with conventional banks; I've never had a problem with my credit union accounts.

Yeah, I should have been clear - accessing it at a local branch. Not that many people need to do that anymore; in fact it's so easy to do everything online you may forget to update addresses, etc. And with no paper statements, you might not even notice until one day your bank decides it needs to mail you something important.

No, I can access my remote credit union account through most credit unions through shared branching. It's more convenient than banks which have less cooperation.